1. Field of the Invention
The invention relates to a converter linking different interfaces, and more particularly, to a converter of a universal serial bus (USB) interface that converts legacy peripherals into hot plug-and-play (hot PnP) peripherals.
2. Description of Related Art
Every since the XT and the later AT personal computers were developed by IBM.RTM., IBM.RTM.-compatible personal computers have been widely used worldwide. In accordance with the advancement of semiconductor technique, usage of a personal computer is more powerful than ever, and the number of peripherals available for a personal computer has increased as well. Examples of peripherals used with personal computers include a mouse, required because of the popularity of graphic user interface, a printer for printing out information, a modem for connecting to the internet, a backup system of a huge capacity to store data periodically in order to prevent data, and a scanner to save graphics into a personal computer. Since each of the foregoing devices is developed independently at different points in time for different purposes, the interfaces used are different with respect to different considerations. Presently every personal computer is equipped with a number of different interfaces so that different peripherals can be used. Some of those equipped interfaces are already set as industrial standards, such as the RS232 serial interface for a mouse and the parallel port for a printer. On the other hand, some of those interfaces also require installation of interface cards, such as the small computer system interface (SCSI) used by most huge-capacity backup devices. Some of the interfaces for a personal computer further require special interfaces, such as the interfaces used by scanners. As a result, each personal computer contains a number of slots for the installation of different interfaces, that makes the cabling and connections of a personal computer and the attached peripherals very messy and complicated.
In view of the foregoing situation, a standard USB interface is then developed, so that all peripherals designed for a personal computer can be connected through a unique interface to simplify the installation of a personal computer system. The reserved space within a personal computer used for the installation of different interface cards is also reduced. The USB interface is plug-and-play, so it can further detect the attached devices and install required drivers for the detected devices.
When a legacy device is installed into a conventional personal computer that uses legacy peripherals. the system must be rebooted as the final step of the entire installation after setting up the newly installed device. When a legacy device is removed, the system cannot automatically detect the absence of the removed device, so the system gives error messages, or even locks up at the moment when the system is trying to execute a program related to the removed device. However, when the system includes a function of hot plug-and-play using the USB interface, the system can automatically detect newly added or removed devices, and then install or uninstall needed drivers and related programs without rebooting the system.
Although employing the USB interface provides a number of advantages, some peripherals are still connected through old-type interfaces, which predate the USB interface. In order to connect those peripherals, which use old interfaces other than the USB interface, to a personal computer through USB interface, a converter is then developed according to the needs.
A PnP peripheral has to have an internal pull-up resistor to be connected to the signal line of the USB interface. When a peripheral is connected to a personal computer through a USB interface the pull-up resistor within the peripheral changes the voltage level on the signal line of the USB interface to instruct the system to start the detection of new devices. As the detection of new device starts, the system first sends out some requests, and devices respond with corresponding descriptors so that the system is able to recognize the present devices, and accomplishes the PnP task. Because the initializations of some peripherals are not finished, or the electrical interfaces are not stabilized while receiving the requests from the system, the requests from the system then cannot be processed correctly. Therefore, the pull-up resistor within a peripheral is preferably connected to the USB interface after the peripheral is initialized and stabilized to reduce the occurrence of detecting errors.
Although some existing converters allow the peripherals using old interfaces to be connected to a personal computer through a USB interface, the functions of those conventional converters are limited. Those conventional converters can only convert the old interfaces of the peripherals to USB interface and send information about the converter to the system, but cannot send information about the connected peripherals. In addition, a conventional converter cannot accomplish the hot PnP task, either, so the user has no information about the status of the connected peripherals that might cause errors during the execution of related programs. Though the problem can be corrected by employing the rolling method of the software simulation, it lowers the efficiency of the system and wastes system resources. This conventional method is not only against the true spirit of PnP, but also causes compatibility problems.
According to the foregoing description, a conventional USB converter has the following drawbacks:
1. A conventional USB converter can only convert the information transferred between interfaces, so the system can obtain the information about the converter but not about the connected peripheral.
2. A conventional USB converter cannot accomplish the hot PnP task, so the system cannot automatically detect the connection status of the peripheral and the system. The system might malfunction due to improper uses such as when a user tries to execute a program on a peripheral, which is not connected to the system. Even though a software simulation can improve the described problems, it affects the efficiency of the system and further might cause compatibility problems.